In the last two years, Mexican President Felipe Calderon has deployed more than 40,000 troops, along with federal police, in a crackdown on drug gangs in the country.

The initiative is part of a $1.6bn (£1.1bn) US plan to help train and equip security forces and strengthen justice systems in Mexico, Central America and the Caribbean.

Corruption fears

Mexico is in the midst of a major campaign against immensely powerful cartels that traffic cocaine and other drugs to consumers in the United States, says the BBC's Stephen Gibbs in Mexico City.

Ninety percent of all the cocaine consumed in the United States is believed to reach the country via Mexico.

President Felipe Calderon, has long sought, and been promised, financial aid from Washington to try to defeat the traffickers.

The aid has been held up for months, partly because US legislators were concerned that the money might end up in the hands of corrupt Mexican officials.

None of the $197m which has just been released will be in the form of cash.

Instead equipment is being provided to enable American and Mexican law enforcers to work more closely together.

Forces unleashed

The deal comes at at time when the drug war in Mexico appears to be having increasingly violent.

In Tijuana last weekend, for example, there were 25 murders, including nine decapitations.

What the numbers signify is open to interpretation.

The Mexican Government says that the increased killings are often the result of leaderless drug gangs turning on each other for the fewer spoils that remain.

But some analysts fear that by taking on the drug runners, President Calderon has unleashed forces he arguably will not be able to control.

There is plenty of evidence that Mexican law enforcement agencies have been extensively infiltrated by the cartels.

The government is having to rely on the army to police parts of the country.

Mr Calderon says his war on drugs will be long and difficult. In that, he is being proved right, our correspondent says.